This invention relates to an engine and more particularly to an improved control for an engine and an arrangement for facilitating feedback control to maintain good fuel economy and good exhaust emission.
It has been recognized that there are a number of advantages in employing gaseous fuel internal combustion engines. Such engines run on a gaseous fuel which is stored under a highly compressed state, frequently as a liquid and which is vaporized and mixed in a charge former for forming a fuel air charge for engine operation. The operation of engines on gaseous fuels conserves natural resources and also can have ecological advantages in that it offers better exhaust emission control. In addition, such fuels have also been found to lengthen the life of the engine.
One particularly advantageous system is disclosed in U.S. Pat. No. 5,337,722, entitled "Fuel Control and Fuel Feed System for Gas Fueled Engine," issued Aug. 16, 1994 and assigned to the assignee hereof. This system employs an exhaust combustion sensor which senses the air/fuel ratio and provides a signal which permits feedback control to maintain the fuel/air ratio under stoichiometric or .lambda.1 conditions throughout the engine running. .lambda.1 is referred to as the ratio of the actual air/fuel ratio to the ideal stoichiometric air/fuel ratio at a given running condition. In the aforenoted patent, that is achieved through the use of an oxygen sensor in the exhaust which outputs a signal when the fuel/air mixture is rich.
As noted in that patent, the oxygen sensor must reach a certain temperature before it will output a signal. Therefore, cold starting cannot be accomplished with the feedback control since the sensor will not output a signal indicative of the fuel/air ratio. In addition, it is necessary to determine when the sensor is operating so as to provide an output signal so that the system can be switched over to a feedback control.
In accordance with the arrangement shown in that patent, a separate circuit is provided for bleeding additional gaseous fuel to the engine during cold starting and cold running so as to ensure that the oxygen center will output a rich signal as soon as the sensor reaches operating temperature.
However, that arrangement is somewhat complicated in that it requires additional fuel circuit and control therefor. In addition, the system requires rich running during cold starting and cold warmup and thus emission control and efficiency is deteriorated.
It is, therefore, a principle object of this invention to provide an improved method and apparatus for a system in the cold starting operation of an engine having feedback control.
It is a further object of this invention to provide an improved feedback control system and method for an engine wherein the sensor can be periodically tested during the warmup operation to determine when it is at operating temperature so that feedback control can be employed.
It is a further object of the invention to provide an improved method and apparatus for performing this function without necessitating a constantly rich mixture during warmup.